Crystal growth mechanism of size-dependent systems in a fluidized bed.

Abstract

Based on the two-step model, surface-integration coefficients of potassium alum crystals below 5 × 10–4 m grown in a well-suspended fluidized bed were found to decrease sharply with decreasing crystal size so that the growth process is controlled by surface integration for small crystals. The mass-transfer coefficient is independent of crystal size and solution velocity. The mass-transfer resistance becomes significant when crystal size increases, and finally the growth rates become constant since both mass-transfer and surface-integration coefficients are constant. For larger crystals, there is no dominating step in the growth process, both resistances being important.The crystal growth behavior of various systems other than potassium alum was also examined. Finally, an experimental method for estimating the order of surface-integration rate is suggested.